"Patients with very low Vitamin D plasma levels had more elevated D-Dimer values, a more elevated B lymphocyte cell count, a reduction of CD8 + T lymphocytes with a low CD4/CD8 ratio, more compromised clinical findings"
A 10x increase in mortality risk with severe Vitamin D deficiency versus those who tested above 10 ng/mL (which is equal to the other common method measuring of Vit D at 25 nmol/L). 25 is very low. You should aim to be above 50.
New study as of Oct '22 from the University of South Australia. It's not specific to Covid, but took long term data (including respiratory disease related mortality) to conclude low levels of Vitamin D are directly linked to premature death. sciencedaily.com/releases/2022/…
An extremely well done thread on Vitamin D that deserves your attention. There's a lot of great info here, including the specific mechanisms of why Vitamin D from sunlight (UVB) is so important.